Cation radicals, borenium cations, and a dication from the oxidation of B-tolyl BIII subporphyrins

Abstract

Oxidation of B-tolyl B^III 5,10,15-tritolylsubporphyrin with tris(4-bromophenyl)ammoniumyl hexachloroantimonate gave its cation radical instantaneously, which slowly dissociated to give B^III subporphyrin borenium hexachloroantimonate in 89% yield after stirring overnight. This is a much more convenient method for the synthesis of B^III borenium cations than the previous synthesis with [Et₃Si]⁺[CH₆B₁₁Br₆]⁻. Oxidants such as tris(4-bromophenyl)ammonium tetrakis(perfluorophenyl)borate and AgSbF₆ can be used for the synthesis of the borenium cation. Oxidation of B-tolyl B^III 5,10,15-trianisylsubporphyrin with AgSbF₆ gave a cation radical that was stable at room temperature but dissociated to give the corresponding borenium cation upon refluxing in CH₂Cl₂, while the B-tolyl B^III 5,10,15-tris(4-dibutylaminophenyl)subporphyrin was oxidized to give a cation radical that was easily oxidized to afford a quinonoidal dication. Oxidation of B-tolyl B^III β-hexaethyl-5,10,15-tri(4-diethylaminophenyl)subporphyrin with AgSbF₆ gave a borenium cation instantaneously. As such, the reactivities of the cation radicals depend on the peripheral substituents.